Dynamic stabilization members with elastic and inelastic sections

ABSTRACT

An improved dynamic longitudinal connecting member includes a rod portion joined with a tensioned cord portion, for use in a medical implant assembly having at least two bone attachment structures, a spacer covering the join of the rod and cord portions and extending between the at least two bone attachment structures, a sleeve, a bumper and a cord blocker. The spacer and bumper are compressed. The cord portion is slidable with respect to at least one of the bone attachment members.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/402,942, filed Sep. 9, 2010; which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention is directed to dynamic fixation assemblies for usein bone surgery, particularly spinal surgery, and in particular tolongitudinal connecting members for such assemblies, the connectingmembers being attached to at least two bone fasteners.

Historically, it has been common to fuse adjacent vertebrae that areplaced in fixed relation by the installation therealong of bone screwsor other bone attachment members, or bone anchors, and cooperatinglongitudinal connecting members or other elongate members. Fusionresults in the permanent immobilization of one or more of theintervertebral joints. Because the anchoring of bone screws, hooks andother types of anchors directly to a vertebra can result in significantforces being placed on the vertebra, and such forces may ultimatelyresult in the loosening of the bone screw or other anchor from thevertebra, fusion allows for the growth and development of a bonecounterpart to the longitudinal connecting member that can maintain thespine in the desired position even if the implants ultimately fail orare removed. Because fusion has been a desired component of spinalstabilization procedures, longitudinal connecting members have beendesigned that are of a material, size and shape to largely resistflexure, extension, torsion, distraction and compression, and thussubstantially immobilize the portion of the spine that is to be fused.Thus, longitudinal connecting members are typically uniform along anentire length thereof, and usually made from a single or integral pieceof material having a uniform diameter or width of a size to providesubstantially rigid support in all planes.

Fusion, however, has some undesirable side effects. One apparent sideeffect is the immobilization of a portion of the spine. Furthermore,although fusion may result in a strengthened portion of the spine, italso has been linked to more rapid degeneration due to increasedstresses and even hyper-mobility and collapse of spinal motion segmentsthat are adjacent to the portion of the spine being fused, reducing oreliminating the ability of such spinal joints to move in a more normalrelation to one another. In certain instances, fusion has also failed toprovide pain relief.

An alternative to fusion and the use of more rigid longitudinalconnecting members or other rigid structure has been a “soft” or“dynamic” stabilization approach in which a flexible loop-, S-, C- orU-shaped member or a coil-like and/or a spring-like member is utilizedas an elastic longitudinal connecting member fixed between a pair ofpedicle screws in an attempt to create, as much as possible, a normalloading pattern between the vertebrae in flexion, extension,distraction, compression, side bending and torsion. Problems may arisewith such devices, however, including tissue scarring, lack of adequatespinal support and lack of fatigue strength or endurance limit. Fatiguestrength has been defined as the repeated loading and unloading of aspecific stress on a material structure until it fails. Fatigue strengthcan be tensile or distraction, compression, shear, torsion, bending, ora combination of these.

Another type of soft or dynamic system known in the art includes boneanchors connected by flexible cords or strands, typically made from aplastic material. Such a cord or strand may be threaded throughcannulated spacers that are disposed between and in contact withadjacent bone anchors when such a cord or strand is implanted, tensionedand attached to or compressed against the bone anchors. The spacerstypically span the distance between the bone anchors, providing limitson the bending movement of the cord or strand and thus strengthening andsupporting the overall system. Such cord or strand-type systemstypically require specialized bone anchors and tooling for tensioningand holding the chord or strand in the bone anchors. Thus a majordisadvantage of such cord and spacer systems is their lack ofinterchangeability with more rigid rod systems, especially those systemsthat incorporate polyaxial screws as bone anchors.

The complex dynamic conditions associated with spinal movement thereforeprovide quite a challenge for the design of more flexible and/or elasticelongate longitudinal connecting members that exhibit an adequatefatigue strength to provide stabilization and protected motion of thespine, without fusion, and allow for some natural movement of theportion of the spine being reinforced and supported by the elongateelastic or flexible connecting member. A further challenge aresituations in which a portion or length of the spine requires a morerigid stabilization, possibly including fusion with deformitycorrection, while another portion or length may be better supported by amore dynamic component that allows for protected movement or stressrelief, especially adjacent to a long rigid rod construct. In such casesa more rigid longitudinal connecting member can be attached to a cordmember of varying length.

SUMMARY OF THE INVENTION

An improved dynamic longitudinal connecting member according to theinvention, for use in a medical implant assembly having at least twobone attachment members cooperating with the dynamic longitudinalconnecting member, is provided. The improved connecting member includesa first end, a transition portion and a second end. A substantiallyrigid rod portion extends longitudinally from the first end to thetransition portion, and includes a longitudinal axis and a substantiallyrigid core running substantially parallel with the longitudinal axis. Asubstantially flexible cord portion is joined with the rigid rod portionand extends from the transition portion to the second end. Asubstantially flexible jacket portion covers the rod and cord portions.

In a further embodiment, the rod portion includes a plurality ofsubstantially rigid longitudinally extending rodlets. In someembodiments, the rod portion includes a binding material adapted forjoining the rodlets together. In some embodiments, the rod portionincludes a plurality of filamentous structures. In some furtherembodiments, the filamentous structures at least partially surround therodlets. In some further embodiments, the filamentous structures aresubstantially flexible. In some further embodiments, the filamentousstructures include at least one polymer.

In a further embodiment, the cord portion is in tension.

In a further embodiment, the cord portion includes a plurality ofsubstantially flexible strands extending from about the transitionportion towards the second end. In some embodiments, the strands arebraided. In some embodiments, the strands are coiled. In someembodiments, the strands are random. In some embodiments, the strandsare embedded in an elastomer. In some embodiments, the strands include apolymer. In some embodiments, the strands include a mixture of a polymerand a plurality of at least one of fibers and filaments.

In a further embodiment, the cord portion is a substantially elasticpolymer filament.

In a further embodiment, the cord portion is a polymer rod. In someembodiments, the polymer rod includes a substantially elastic polymer.In some embodiments, the polymer rod includes a composite of at leasttwo polymers.

In a further embodiment, the cord portion includes a flexible cable.

In a further embodiment, the cord portion includes a flexible cord.

In a further embodiment, a spacer covers the transition portion. In someembodiments, the spacer extends between the at least two bone attachmentmembers. In some embodiments, the spacer is substantially elastic.

In a further embodiment, a sleeve is located between the cord portionand one of the at least two bone attachment members. In someembodiments, the sleeve includes a through-bore in sliding engagementwith the cord portion.

In a further embodiment, the rod portion is an inelastic stent structureat least partially embedded in an elastomer. In some embodiments, therod portion includes a substantially cylindrical outer surface; and thestent structure includes a longitudinally extending lumen and aplurality of longitudinally oriented concave grooves adapted forcontacting the elastomer. In some embodiments, the stent structureincludes a plurality of bores extending radially from the lumen to oneof the plurality of concave grooves. In some embodiments, the cordportion includes a substantially flexible rod formed of the elastomer;and wherein the elastomer fills the lumen and the bores.

In a further embodiment, the assembly includes an elastic bumper and acord blocker.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings constitute a part of this specification and includeexemplary embodiments of the present invention and illustrate variousobjects and features thereof.

FIG. 1 is a front elevational view of a dynamic fixation longitudinalconnecting member assembly according to the invention showing a dynamicfixation longitudinal connecting member according to the invention shownattached to three polyaxial bone screws of the invention.

FIG. 1 a is a top view of the assembly of FIG. 1.

FIG. 2 is an exploded, reduced front elevational view of the dynamicfixation longitudinal connecting member assembly of FIG. 1 shown withoutthe polyaxial bone screws, the assembly including a dynamic fixationlongitudinal connecting member having rod and cord portions, an elasticspacer, a rigid sleeve, an elastic bumper, and a cord blocker with setscrew.

FIG. 3 is an enlarge cross-sectional view of the assembly of FIG. 1,taken on line 3-3 of FIG. 1 a.

FIG. 4 is front elevational view of the dynamic fixation longitudinalconnecting member of FIG. 1, with portions broken away to show detailthereof, including a rod portion and a cord portion.

FIG. 5 is an enlarged cross-sectional view of the dynamic fixationlongitudinal connecting member of FIG. 4, taken along the line 5-5 ofFIG. 4.

FIG. 6 is front elevational view of a second embodiment of a dynamicfixation longitudinal connecting member according to the invention, withportions broken away to show detail thereof, including two cord portionsjoined by a rod portion.

FIG. 7 is a perspective view of a third embodiment of a dynamic fixationlongitudinal connecting member according to the invention, including arigid first rod portion and an elastic second rod portion, with portionsbroken away to show detail thereof.

FIG. 8 is an enlarged cross-sectional view of the dynamic fixationlongitudinal connecting member of FIG. 7, taken along the line 8-8 ofFIG. 7.

FIG. 9 is a perspective view of a fourth embodiment of a dynamicfixation longitudinal connecting member according to the invention,including a rigid first rod portion and an elastic second rod portion.

FIG. 10 is an enlarged left side view of the dynamic fixationlongitudinal connecting member of FIG. 9.

FIG. 11 is an enlarged cross-sectional view of the dynamic fixationlongitudinal connecting member of FIG. 9, taken along the line 11-11 ofFIG. 9.

FIG. 12 is a front elevational view of the dynamic fixation longitudinalconnecting member of FIG. 9, shown with four bone attachment members andtwo spacers according to the invention, with portions shown in phantomto show detail thereof.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It is also noted that any reference tothe words top, bottom, up and down, and the like, in this applicationrefers to the alignment shown in the various drawings, as well as thenormal connotations applied to such devices, and is not intended torestrict positioning of the bone attachment members in actual use.

With reference to FIGS. 1-5 the reference number 1 generally designatesa non-fusion dynamic stabilization longitudinal connecting memberassembly according to the present invention. The connecting memberassembly 1 generally includes a dynamic longitudinal connecting member 2in cooperation with at least two bone attachment members 4, such as bonescrews, anchors or hooks, as described below with reference to FIG. 1.The longitudinal axis of the assembly 1 is denoted by the letter A.

The connecting member 2 extends longitudinally from a first end 6 to asecond end 8 thereof, with a transition portion 10 located therebetween.The connecting member 2 is substantially cylindrical, with asubstantially circular cross-section. The diameter of the connectingmember 2 is sized for engagement by the bone attachment members 4 and issubstantially uniform, constant or unchanging, along its length, withoptional exceptions discussed below. It is foreseen that the connectingmember 2 may have other forms, including but not limited to oval, squareand rectangular cross-sections as well as other curved or polygonalshapes.

The connecting member 2 includes rod and cord portions 12 and 14. Therod and cord portions 12 and 14 have differing relative level ofrigidity, flexibility or deformability, depending upon the supportrequirements of the implant assembly 1. Generally, the rod portion 12 ismore rigid and less deformable than the cord portion 14. A flexiblejacket portion 16 covers the connecting member 2, providing asubstantially smooth, strong and resilient outer surface thereto.

Referring to FIGS. 4-5, the rod portion 12 is a substantially rigidrod-shaped structure extending longitudinally from the first end 6 tothe transition portion 10. The rod portion 12 is of a length forcooperating with at least one and up to a plurality of bone attachmentmembers 4, such as bone screws or hooks, and may be cut to the desiredlength during implantation. For example, in FIGS. 1 and 3, the rodportion 12 is shown cooperatively engaged by two bone anchors 4. The rodportion 12 has a substantially circular cross-section along its length,with a diameter sufficient for engagement by the bone anchor(s) 4.Generally, the diameter of the rod portion 12 is substantially uniform,or constant, along the length thereof. It is foreseen, however, that therod portion 12 may have other forms, including but not limited to oval,square and rectangular cross-sections as well as other curved orpolygonal shapes.

The rod portion 12 includes a substantially rigid core 16 that runssubstantially parallel with the longitudinal axis A, from the first end6 to the transition portion 10. The core 16 includes a plurality of verythin, long, cylindrical rodlets, some of which are denoted by thenumerals 20 a, 20 b, 20 c and 20 d.

The longitudinally extending rodlets 20 a, 20 b, 20 c and 20 d arebundled or grouped together. A sufficient number of the rodlets 20 a, 20b, 20 c and 20 d is included in the bundle so as to render the rodportion 12, as a whole, substantially rigid or non-elastic. Generally,the individual rodlets 20 a, 20 b, 20 c and 20 d are formed of asubstantially hard, stiff, non-elastic material, such as a metal or ahard plastic. However, it is foreseen that at least some of the rodlets20 a, 20 b, 20 c and 20 d may be elastic, flexible, or otherwisedeformable. It is noted that, while individual rodlets 20 a, 20 b, 20 cand 20 d may be somewhat bendable or deformable due to their thinness,when grouped together the rodlets convey strength, rigidity andresilience to the rod portion 12 while simultaneously retaining a smalldegree of flexibility and a capacity to absorb and/or transmit forcesapplied thereto.

While in the illustrated embodiment, all of the rodlets 20 have the samecylindrical geometry, including the same diameter and smooth,cylindrical surfaces, it is foreseen that some or all of the rodlets 20may vary in geometric shape, especially in diameter, and/or material offabrication so as to provide various desired levels of rigidity to therod portion 12. For example, a more rigid rod portion 12 may includeharder rodlets, while a less rigid rod portion 12 may include moreflexible rodlets.

The rodlets 20 a, 20 b, 20 c and 20 d may be made from may be made of avariety of materials ranging from deformable plastics to hard metals,depending upon the desired application. Suitable materials include, butare not limited to metals, metal alloys and deformable and lesscompressible plastics, including, but not limited to stainless steel,titanium, titanium alloys and cobalt chrome; and plastic polymers suchas polyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene(UHMWP), polyurethanes and composites, including composites containingcarbon fiber, natural or synthetic elastomers such as polyisoprene(natural rubber), and synthetic polymers, copolymers, and thermoplasticelastomers, for example, polyurethane elastomers such aspolycarbonate-urethane elastomers. It is foreseen that in someembodiments, some or all of the rodlets 20 a, 20 b, 20 c and 20 d may bedeformable and/or of a different cross-sectional geometry. Further, itis foreseen that the geometry and fabrication material of the individualrodlets 20 a, 20 b, 20 c and 20 d may be varied such that, when bundledtogether, the rod portion 12 is provided a desired level of rigidity orflexibility.

As shown in FIG. 5, the rodlets 20 a, 20 b, 20 c and 20 d include asubstantially circular cross-section with substantially equal diameters,and are spaced relative to one another. The rodlets 20 a, 20 b, 20 c and20 d may be joined together using various techniques, structures and/ormeans. For example, the rodlets 20 a, 20 b, 20 c and 20 d may be fusedtogether, such as by heat, compression or friction welding, or even bywrapping with a strand or thread-like structure. In other circumstances,a binding material 22, such as an adhesive or an elastomer may join therodlets 20 a, 20 b, 20 c and 20 d together. For example, the rodlets 20a, 20 b, 20 c and 20 d may be embedded in a polymer material or matrix,such as but not limited to plastic polymers such as polyetheretherketone(PEEK), ultra-high-molecular weight-polyethylene (UHMWP), polyurethanesand composites, including composites containing carbon fiber, natural orsynthetic elastomers such as polyisoprene (natural rubber), andsynthetic polymers, copolymers, and thermoplastic elastomers, forexample, polyurethane elastomers such as polycarbonate-urethaneelastomers.

Additionally or alternatively, a plurality of filamentous structures atleast partially surround and/or hold and/or bind the rodlets, so as toimpart increased tensile strength and resiliency to the rod portion 12.In FIG. 5, exemplary filamentous structures are denoted by the numerals24 a, 24 b, 24 c and 24 d. The filamentous structures 24 a, 24 b, 24 cand 24 d are somewhat flexible, bendable or otherwise deformablethreads, fibers, fibrils or microfibers of various lengths,cross-sectional shapes and diameters. The filamentous structures 24 a,24 b, 24 c and 24 d randomly bend about the rodlets 20 a, 20 b, 20 c and20 d, so as to form a non-woven, tangled, mesh-like structure thatsecures the rodlets 20 a, 20 b, 20 c and 20 d and strengthens the rodportion 12. Filamentous structure 24 a, 24 b, 24 c and 24 d having awide range of dimensions are foreseen. Further, instead of beingrandomly tangled, it is foreseen that some or all of the filamentousstructures 24 a, 24 b, 24 c and 24 d may be elongate and aligned withthe rodlets 20 a, 20 b, 20 c and 20 d.

The filamentous structures 24 a, 24 b, 24 c and 24 d may be fabricatedof a variety of materials, such as but not limited to polymers andminerals. Suitable polymers include but are not limited to plasticpolymers such as polyetheretherketone (PEEK), ultra-high-molecularweight-polyethylene (UHMWP), polyurethanes and composites, includingcomposites containing carbon fiber, natural or synthetic elastomers suchas polyisoprene (natural rubber), and synthetic polymers, copolymers,and thermoplastic elastomers, for example, polyurethane elastomers suchas polycarbonate-urethane elastomers. Suitable minerals include carbonand certain metals.

It is noted that in some circumstances, the filamentous structures 24 a,24 b, 24 c and 24 d are the binding material 22; no adhesive orelastomeric binder is included. In other circumstances, the bindingmaterial 22 is a blend of a base polymer with a plurality of filamentousstructures 24 a, 24 b, 24 c and 24 d distributed therein. For example, abinding material 22 of a polycarbonate-urethane elastomer and carbonfibers may secure the rodlets 20 a, 20 b, 20 c and 20 d together, so asto form the core 18 of the rod portion 12.

The cord portion 14 extends longitudinally from the transition portion10 to the second end 8. The cord portion 14 is substantially cylindricalwith a smooth outer surface. The cord portion 14 includes substantiallycircular cross-section and a substantially uniform, or constant,diameter along its length, the diameter being sufficient to be receivedby the bone anchor(s) 4. It is noted that the diameter, or width, of thecord portion 14 is generally less than or equal to the diameter of therod portion 12. However, in some circumstances, the diameter of the cordportion 14 may be greater than the diameter of the rod portion 12. It isforeseen that the cord portion 14 may have other forms, including butnot limited to oval, square and rectangular cross-sections as well asother curved or polygonal shapes.

The cord portion 14 is strong and flexible, elastic or deformable. Thecord portion 14 includes a length sufficient for engagement by at leastone, two or more bone attachment members 4, and may be cut to thedesired length during implantation. Optionally, the cord portion 14includes an additional tapered portion, located at the second end 8.Such a tapered portion may ease threading the second end 8 through theeye of a closed headed bone anchor 4, tensioning thereof, andsubsequently cut off after completion of implantation of the assembly 1.

The cord portion 14 may be made from a variety of materials, includingpolyester or other plastic fibers, strands or threads, such aspolyethylene-terephthalate. A cord according to the invention typicallydoes not illustrate elastic properties, such as any significantadditional axial distraction and lengthening after the assembly 1 isoperatively assembled and the cord portion 14 is tensioned. However, itis foreseen that in some embodiments, the cord portion 14 may be made ofan elastic or semi-elastic material, such as a plastic or rubber(natural or synthetic) having at least some elastic properties, allowingfor some further distraction of the assembly 1 during operation thereof.The cord portion 14 can also be a cable-like structure made of metal.Suitable hinged and fixed bone attachment members 4 for mating with thecord portion 14, or with the rod portion 12, are described inApplicant's U.S. patent application Ser. No. 11/328,481 filed Jan. 9,2006, Publication No. 20060111715, incorporated by reference herein.

The cord portion 14 includes a plurality of substantially flexible,resilient strands. Exemplary strands are denoted by the numerals 26 a,26 b, 26 c and 26 d. The strands 26 a, 26 b, 26 c and 26 d may befabricated from a variety of materials having various degrees ofelasticity, depending upon the application. Suitable materials includebut are not limited to a polymer, such as polyester or other plasticfibers, strands or threads, such as polyethylene-terephthalate. In somecircumstances, the strands 26 a, 26 b, 26 c and 26 d are fabricated fromsubstantially elastic or deformable polymers, such as but not limited tonatural or synthetic elastomers such as polyisoprene (natural rubber),and synthetic polymers, copolymers, and thermoplastic elastomers, forexample, polyurethane elastomers such as polycarbonate-urethaneelastomers. In certain embodiments, the strands 26 a, 26 b, 26 c and 26d are formed of a metal or metal alloy, such as but not limited tostainless steel, titanium, titanium alloys, and carbon.

Alternatively or additionally, some or all of the strands 26 a, 26 b, 26c and 26 d may be formed of an extruded or spun mixture of a basepolymer with polymer or mineral fibers, fibrils or filaments. In anexemplary embodiment, the strands 26 a, 26 b, 26 c and 26 d arefabricated by extruding and curing a mixture of carbon fibers orfilaments, and a polymer binder, including but not limited to plasticpolymers such as polyetheretherketone (PEEK), ultra-high-molecularweight-polyethylene (UHMWP), polyurethanes and composites, includingcomposites containing carbon fiber, natural or synthetic elastomers suchas polyisoprene (natural rubber), and synthetic polymers, copolymers,and thermoplastic elastomers, for example, polyurethane elastomers suchas polycarbonate-urethane elastomers. It is foreseen that includingstrands formed of various materials may provide a cord portion 14 withunique characteristics, such as strength, resilience, deformability,flexibility and/or rigidity.

The strands 26 a, 26 b, 26 c and 26 d may be woven, braided, coiled,twisted, plaited, bonded or otherwise joined to grouped together, so asto form the strong and flexible cable, cord or rope of the cord portion14. Alternatively, as shown in FIG. 6, the strands 26 may be randomlyarranged, and optionally bonded, so as to form a somewhat tangled mass,non-woven web or matrix, or similar grouping. In some embodiments, thestrands 26 a, 26 b, 26 c and 26 d are embedded in an elastomer, such asdescribed above with respect to the binding material 22 and/or thestrand fabrication material, above.

In some embodiments, the cord portion 14, or the strands 26 a, 26 b, 26c and 26 d, simply abuts the rod portion 12 at the transition portion10. In other embodiments, strands 26 a, 26 b, 26 c and 26 d areextensions of the filamentous structures 24 a, 24 b, 24 c and 24 d. Forexample, the filamentous structures 24 a, 24 b, 24 c and 24 d may bestrands 26 a, 26 b, 26 c and 26 d that extend from about the first end 6of the connecting member 2, through the transition portion 10, and toabout the second end 8.

In an exemplary embodiment, each strand 26 a, 26 b, 26 c and 26 dincludes a length about equal to the length of the connecting member 2.A first portion, of each of the strands 26 a, 26 b, 26 c and 26 d, isaligned, interspersed and bundled with the rodlets 20 a, 20 b, 20 c and20 d, and optionally fused and/or embedded in the binding material 22.The second portion, of each of the strands 26 a, 26 b, 26 c and 26 d,extends from the rod portion 12, past the transition portion 10, and toabout the second end 8 of the connecting member 2. The strand secondportions may be braided, twisted, plaited, bonded and/or embedded in apolymer, such as into a strong cord-like or cable-like structure, suchas described elsewhere herein.

A flexible jacket portion 16 is disposed over and optionally attached tothe rod and cord portions 12 and 14 of the connecting member 2. Thejacket portion 16 is preferably very strong, flexible and resistant tofraying and degradation during the operable lifetime, or the duration ofimplantation, of the connecting member 2. Generally, the jacket portion16 is a woven layer snugly covering the connecting member 2. However, itis foreseen that the jacket portion 16 may be a non-woven layer, such asa tangled mesh of fibers or a polymer film. The jacket portion 16 may bejoined, tightly bound or adhered to the connecting member 2, such as byan adhesive or by heat or pressure welding. Alternatively, the jacketportion 16 may be so tightly woven or otherwise formed around the rodand cord portions 12 and 14 that movement of the jacket portion 16 withregards to the rod and cord portions 12 and 14 is substantially blocked

The jacket portion 16 may be fabricated of a variety of strong, flexiblematerials. In order to have low or no wear debris, the jacket outersurface may be coated with an ultra thin, ultra hard, ultra slick andultra smooth coating, such as may be obtained from ion bondingtechniques and/or other gas or chemical treatments. Cooperating portionsof an engaging attachment member 4 may also be coated with the ultrathin, ultra hard, ultra slick and ultra smooth coating.

With reference to FIGS. 1-3, a dynamic stabilization longitudinalconnecting member 2 according to the invention is shown attached tothree polyaxial bone screws, generally 4. The connecting member 2 iselongate and substantially cylindrical, having a substantially centrallongitudinal axis A. On the right-hand side of FIG. 1, a first polyaxialbone screw 4 engages the rod portion 12 of the connecting member 2 so asto be located adjacent to the first end 6 thereof. A second, or middle,engaging polyaxial bone anchor 4 is located between the first boneanchor 4 and the transition portion 10. The third, or left-hand,engaging polyaxial bone anchor 4 is located to the left of thetransition portion 10 and adjacent to the second end 8. It is noted thatthe transition portion 10 is not directly engaged by a bone anchor 4.Instead, the transition portion 10 is located between two bone anchors4.

Initially, one or both of the rod and cord portions 12 and 14 may besubstantially longer than required in the completed implant assembly 1,or as shown in FIGS. 1-3. For example, one or both of the rod and thecord portions 12 and 14 may include a length sufficient for engagementby 2, 3, 4 or more bone anchors 4. Additionally, one or both of the rodand cord portions 12 and 14 may include an extra length for graspingwith a tool and tensioning the connecting member 2. In somecircumstances, such and extension is tapered, to aid in threading therod or cord portion 12 or 14 through a bone anchor 2, and the like.Accordingly, the rod and cord portions 12 and 14 may be cut to desiredlengths during an implantation procedure.

Because the connecting member 2 is substantially solid and cylindrical,it may be used with a wide variety of bone anchors already available forcooperation with rigid rods including fixed, monoaxial bone screws,hinged bone screws, polyaxial bone screws, and bone hooks and the like,with or without compression inserts, that may in turn cooperate with avariety of closure structures having threads, flanges, or otherstructure for fixing the closure structure to the bone anchor, and mayinclude other features, for example, break-off tops and inner setscrews. The bone anchors 4, closure structures and the connecting member2 are then operably incorporated in an overall spinal implant system 1for correcting degenerative conditions, deformities, injuries, ordefects to the spinal column of a patient. Several suitable hinged andfixed bone screws 4 for mating with the connecting member 2 of thepresent invention are described in Applicant's U.S. patent applicationSer. No. 11/328,481 filed Jan. 9, 2006, Publication No. 2006-0111715;U.S. patent application Ser. No. 12/661,042 filed Mar. 10, 2010.; andU.S. patent application No. 61/336,991 filed Jan. 28, 2010, each ofwhich is incorporated by reference herein.

Each of the polyaxial bone screws 4 includes a threaded shank 152 forattachment to bone (not shown), a receiver 154 that is adapted toreceive the connecting member 2, and a closure top 156 that locks thebone screw 4 into a fixed position. In some circumstances, a slide orslipping closure top 156, with a substantially flat bottom surface 156 ais used to slidingly secure connecting member cord portion 14 in thereceiver 154. In some circumstances, a non-sliding closure 156 may beemployed with the cord portion 14, so as to lock the cord portion in thereceiver 154. In other circumstances, a point and rim closure topclosure top 156, with a bottom surface 156 b having a structure thatcontacts, grips and fixedly engages the rod portion 12, is used to lockthe connecting member rod portion 12 in the receiver 154. A detaileddescription of these types of closure tops can be found in Applicant'sco-pending U.S. patent application Ser. No. 12/661,042 filed Mar. 10,2010, incorporated herein by reference.

In addition to the bone screws 4 and the connecting member 2, theillustrated connecting member assembly 1 generally includes at least ahard, inelastic flanged sleeve 158, an elastic spacer 160, an optionalrigid spacer liner (not shown), an elastic bumper 162 and a cord blocker164 with cooperating set screw 168. A detailed description of thesestructures can be found in Applicant's co-pending U.S. patentapplication No. 61/336,991 filed Jan. 28, 2010, incorporated herein byreference.

Referring to FIGS. 2-3, the connecting member 2 extends along the axisA, from the first end 6 to the second end 8, and successively throughand within the first and second bone anchors 4, the spacer 160, thesleeve 158, the third bone anchor 4, the bumper 162 and the cord blocker164, for example. As best shown in FIG. 3, the connecting membertransition portion 10 is located between two bone screws 4, so as to notbe directly engaged by a bone screw 4. In the illustrated embodiment,the transition portion 10 is located between the second and third boneanchors 4, as well as within both the sleeve 158 and the spacer 160.

It is noted that in some circumstances, one or both of the rod and cordportions 12 and 14 may be longer than depicted in FIGS. 1-3.Accordingly, a suitable number of additional spacers 160, sleeves 158,and/or bone anchors 4 would be employed with the cooperating connectingmember 2. For example, the rod portion 12 may include a lengthsufficient for engagement by three or more bone anchors 4. Similarly,the cord portion 14 may include a length sufficient for engagement bytwo or more bone anchors 4, including a suitable number of cooperatingsleeves 158 and spacer 160. It is noted that, in some circumstances, anon-sliding closure 156 may be employed cooperatively with a sleeve 158,so as to block sliding axial movement of the sleeve 158 relative to thecore portion 14.

The spacer 160 is substantially elastic, longitudinally extending,cylindrically shaped, with a smooth outer surface 169. The spacer 160 istypically elastic and made from a plastic, for example, a thermoplasticelastomer made from a polyurethane or polyurethane blend, such as apolycarbonate urethane. The spacer 160 is adapted to be cut to length bythe surgeon.

The spacer 160 includes a substantially cylindrical through-bore 170with a smooth inner surface 172 that extends from a first end 174 of thespacer 160 to a second end 176 thereof. The through-bore 170 is sizedand shaped so as to receive the connecting member 2 therethrough. Thethrough-bore 170 diameter is at least slightly greater than that of theconnecting member 2, such that the connecting member 2 may be receivedtherethrough. In some circumstances, the spacer inner surface 172contacts an outer surface 178 of the connecting member 2. In othercircumstances, the through-bore 170 diameter is sized such that thespacer inner surface 172 is spaced from the connecting member outersurface 178. In some circumstances, at least a portion of thethrough-bore 170, or the inner surface 172, is sized and shaped, orgraduated, so as to also receive therein at least one of an optionalliner (not shown) and a portion of the sleeve 158, such as describedbelow. The spacer 160 may include various and graduated inner surfaces172 that are sized and shaped to be press fit over a knobbed feature ofan adjacent sleeve or a liner (not shown).

In the completed assembly 1, the connecting member 2 is received throughthe spacer through-bore 170 such that the transition portion 10 islocated within the spacer 160. The spacer first end 174 is planar andannular, and abuts the receiver 154 of the second, or middle, boneanchor 4. The spacer second end 176 is also planar and annular, andabuts the receiver 154 of the third bone anchor 4 and/or the sleeve 158covering the cord portion 14, such as described below. In somecircumstances, the ends 174 and 176 are non-planar and contoured so asto cooperatively matingly engage the side of the bone anchor receiver154.

A sleeve 158 is received over, or about, the cord portion 14, so as tobe located between the cord portion 14 and the bone anchor receiver 154,so as to protect the cord portion 14 from crushing and degradation. Thesleeve 158 includes a body 180, a longitudinally extending through-bore182, two flanges 184 and 186, a centering body portion 188 between theflanges 184, and a closure-receiving orifice 183 joining the top surfaceof the centering body 188 with the interior surface of the through-bore182. The end surfaces 190 and 192 of the sleeve 158 may substantiallyplanar and annular, or they may sized and shaped, or contoured, so as tocooperatively matingly engage the bone anchor receiver 154. Optionally,the sleeve 158 includes a tubular extension 193 that extends partiallyinto and/or through the spacer through-bore 170. Additionally, oralternatively to the tubular extension 193, the sleeve 158 may include aknobbed structure (not shown) disposed adjacent to the flange 186 and/orthe flange 184. Such a knobbed structure provides a push-on connectiveelement for attachment to inner graduated surfaces of the spacer 160and/or the bumper 162.

It is noted that more than one size of sleeve 158 is typically providedto the surgeon, the sleeves 158 differing only in the length of thetubular extension 193 included, so as to appropriately match the size ofthe patient's spine. A desirable fabrication material for both theoptional liners and the sleeve tubular extensions 193 is cobaltchromium. Furthermore, in some embodiments of the invention, in order tohave low or no wear debris, the liner inner surface and the outersurfaces of the sleeve tubular extensions 193 may be coated with anultra thin, ultra hard, ultra slick and ultra smooth coating, such asmay be obtained from ion bonding techniques and/or other gas or chemicaltreatments. It is further noted that sleeve inner surfaces 194 may alsobe likewise coated to provide a slick, low to no wear debris interfacewith the cord portion 14.

Referring to FIG. 3, the connecting member cord portion 14 is receivedthrough the through-bore 182 and is secured or locked with a slide orslipping closure top 156. The closure top 156 also fixedly locks thesleeve 158 in the bone screw 4. The slide or slip closure top 156engages the sleeve 158 but not the cord portion outer surface 178,allowing the cord portion 14 to slip or slide within the polyaxial screw4. It is foreseen that a grip closure top 156 may be used in place of aslip closure top 156. A grip closure top extends through the sleeve 158and grips and fixes the cord portion 14 against an inner surface 194 ofthe sleeve 158 and thus fixes the cord portion 14 in relation to thepolyaxial screw 4.

A portion of the sleeve 158 may extend into and through the spacer 160and is in slidable relationship therewith. Such spacer overlap withrespect to the sleeve 158 provides advantageous anti-shear support forthe connector 2. A portion of the cord blocker 164 also extends into abore of the bumper 162. The bumper 162 is typically made from anelastomer while the spacer 160, although typically elastomeric, may bemade from a material with a different durometer, typically (but notalways) being tougher and less compressible than the material of thebumper 162. The sleeve 158 and the optional spacer liner are made from ahard, non-elastic material, such as a metal or metal alloy, like cobaltchromium. The hard and stiff sliding sleeve 158 may include an extensionthat slides into the respective liner, providing a dynamic no- orlow-wear, sliding relationship between the sleeve and optionalcooperating liner that is non-binding, and provides excellent shearresistance. At the same time, the thin liner and the cooperatingelastomeric spacer 160, as well as the tensioned cord portion 14,provide controlled bending, with the tensioned cord portion 14 andcompressed bumper 162 performing well under tension and compression. Theflanged portions 184 and 186 of the sleeve 158 are located on eitherside of the bone screw receiver 154, the flange surfaces 190 and 192abutting against the spacer 160 and the bumper 162, the flanges 184 and186 extending radially outwardly to an extent to fully engage the endsof the adjacent spacer 160 or the bumper 162, resulting in a stable,secure, substantially full contact between the individual elements ofthe assembly 1. Furthermore, the flanges 184 and 186 allow for assemblyand dynamic setting of the assembly 1 prior to implantation, if desired,with the cord portion 14 being placed in tension and at least the bumper162 being placed in compression. In some embodiments of the invention,tensioning of the cord portion 14 and compression of the bumper 162 andoptionally the spacer 160 may be performed after the assembly 1 isattached to the bone screws 4.

The bumper 162 is elastic and may be made from a variety of compressibleand stretchable materials, including, but not limited to natural orsynthetic elastomers such as polyisoprene (natural rubber), andsynthetic polymers, copolymers, and thermoplastic elastomers, forexample, polyurethane elastomers such as polycarbonate-urethaneelastomers. In order to have low or no wear debris, the bumper innersurface may also be coated with an ultra thin, ultra hard, ultra slickand ultra smooth coating, such as may be obtained from ion bondingtechniques and/or other gas or chemical treatments.

The cord blocker 164 includes a body portion 196 and a tubular extension198 sized and shaped to be slidingly received in the bumper 162. Theillustrated body portion 196 and tubular extension 198 are integral orotherwise fixed to one another. A through-bore 199 extends through alower portion of the body portion 196 and centrally through the tubularextension 198. The through-bore 199 is sized and shaped to receive thecord portion 14 and when assembled with a remainder of the assembly 1extends along the axis A. Formed in the body portion 196 is a threadedbore 200 sized and shaped to receive and threadably mate with a threadof the cooperating set screw 168. The threaded bore 200 communicateswith the through-bore 199 and is substantially perpendicular thereto. Asurface partially defining the through-bore 199 includes a depression(not shown), sized and shaped for receiving the cord portion 14 thereinwhen the set screw 168 engages the cord portion 14. The sleeve 160 alsoincludes such a depression for receiving the cord portion 14 within thethrough-bore 182 thereof when the grip closure top 165 is used to clampthe cord portion 14 within the sleeve 160 without damaging or destroyingthe cord portion 14.

It is noted that the blocker 164 and set screw 168 combination istypically provided with the bumper 162 pre-attached thereto and handledas a unit assembly. Thus, prior to being received by the surgeon, thebumper 162 is wedged and in some cases adhered or otherwise fixed ontothe tubular extension 198 at the factory, with the inner surface of thebumper frictionally engaging the outer surface of the tubular extension198 and the bumper 162 abutting against and fixed to the blocker body196.

Various closure tops 156 may be used with the bone anchors 4. Suitableclosure tops 156 include a break-off head designed to allow such a headto break from a base of the closure at a preselected torque, forexample, 70 to 140 inch pounds. The closure structure 156 generallyincludes an outer helically wound guide and advancement structure (notshown) that is sized and shaped to rotatably mate with a cooperatinginner helically wound guide and advancement structure (not shown) on thebone screw receiver 154. The bottom surface of the closure top 154 maybe either include a point and rim or be substantially planar. A smoothor flat bottom surface 156 a is designed to not grip and fixedly engagethe connecting member 2, so as to allow sliding of the connecting member2 within the bone screw receiver 154. A point and rim bottom surface 156b is designed to grip and fixedly engage the connecting member 2, so asto block sliding of the connecting member 2 within the bone screwreceiver 154.

The assembly 1 may be assembled as follows: First, after the bone screws4 are implanted, the distance between the screws is measured.Thereafter, the spacer 160, and optional liner, is cut to a desiredlength based upon the measurement made between the bone screws. A tool(not shown), similar to a pipe cutter, is usually used to rotate and cutthe spacer 160 to the desired length at an end opposite the optionalgraduated surfaces of the spacer. Also at this time, in view of theresulting spacer length, a cooperating sleeve 158 of desired size ischosen. Because the sleeve 158 is made from a hard material, typically ametal or metal alloy, it is not practical to cut the tube portion 193 toa desired length during the surgical procedure. Therefore, a variety ofsleeves 158 are typically provided to end users having at least threedifferent tube portion lengths.

With particular reference to FIG. 2, the cord portion 14 is thensuccessively threaded through the connector elements as shown by thearrow G in FIG. 2, some of the components, such as the blocker/bumper164/162 having been previously assembled. As the cord portion 14 isthreaded into the assembly elements, the spacer 160 is placed intoposition covering or overlapping the optional tubular portion 193 of thesleeve 158. The cord portion 14 is typically much longer than shown inFIG. 2 and then cut to length near the end 8 after being fully assembledwith the remaining elements of the assembly 1, so that the cord portion14 may be grasped and tensioned either before or after the assembly 1 isfixed to the bone screw 4. If pre-tensioning is desired, at this time,prior to implanting the assembly, a tensioning tool (not shown) known inthe art is used to pull upon and put tension on the cord portion 14 nearthe end 8. The cord portion 14 is preferably tensioned until the bumper162 compresses and then the set screw 168 is rotated and driven into theblocker 164 and up against the cord portion 14 using a driving tool (notshown) engaged with an inner drive of the set screw 168.

The assembly 1 (either pre-tensioned or in a loosely attachedorientation) is implanted by inserting the sleeve body portions into thebone screws 4 with each receiver 10 being received between the twoflanges of the sleeve 158. Closure tops 156 are chosen by the surgeonbased upon whether a sliding or a gripping relationship is desired withthe particular receiver 154.

With reference to FIG. 1, the final tensioned assembly 1 is shown thatis substantially dynamically loaded and oriented relative to thecooperating vertebra, providing relief (e.g., shock absorption) andprotected movement with respect to flexion, extension, distraction andcompressive forces placed on the assembly 1 and the connected bonescrews 4 as well as providing more rigid support at the rod portion 12.During complex spinal movements, the spacer 160 is able to move or flexaway from and towards the flange 184 of the sleeve 158 withoutcompromising the strength and integrity of the assembly 1. It is notedthat a problem encountered with dynamic spinal implant systems is theneed to provide adequate support with respect to bending sheer. Mostspinal movements are not purely bending movements, e.g., flexion andextension. Most movements include both bending and tension, extension orcompression. Such bending shear is not well resisted by a cord andspacer alone that performs well in tension, but not when the tensionincludes a vector force. The present invention advantageously provides ahard, non-elastic extension of a rigid sliding sleeve body 180, theoptional extension further located within a optional non-elastic linerof the spacer 160. Such features protect against vector forces whilestill allowing for advantageous tension of the cord portion 14 as wellas improved compression provided by the outer bumper 162. The cordportion 14 and the sleeve 158 allow for some twisting or turning,providing some relief for torsional stresses. Furthermore, thecompressed bumper 162 and the fixed contact between the sleeve 158 andthe end of the spacer 160, as well as the fixed contact between thebumper 162 and the blocker 164 places some limits on torsional movementas well as bending movement, to provide spinal support. The cord portion14 (in tension) and bumper 162 (in compression) allow for compressionand some extension of the assembly 1 located between the two bone screws4, e.g., shock absorption. Another advantage of embodiments of thepresent invention is that because of the inelastic sleeve extension 193that slides within and is overlapped by the typically elastic spacer 160located between two bone screws 4, the resulting assembly 1 is morestable than a cord portion 14 and spacer 160 alone, therefore strengthof the assembly 1 does not rely upon the amount of tension placed uponthe cord portion 14. Therefore, in embodiments according to theinvention, it is not necessary to place as much tension on the cordportion 14 as would be required for a more traditional cord and spacerarrangement, thus protecting the cord from damage of over stressing.

If removal of the assembly 1 from any of the bone screw assemblies 4 isnecessary, or if it is desired to release the assembly 1 at a particularlocation, disassembly is accomplished by using the driving tool (notshown) with a driving formation cooperating with internal drives of theclosure structures 156, to rotate and remove such closures from thereceivers 154. Disassembly is then accomplished in reverse order to theprocedure described previously herein for assembly.

Eventually, if the spine requires more rigid support, the connectingmember 2 according to the invention may be removed and replaced withanother longitudinal connecting member, such as a solid rod or bar,having the same width or diameter as body portion 196 of the sleeve 158,utilizing the same receivers 154 and the closure structures 156.Alternatively, if less support is eventually required, a less rigid,more flexible assembly, for example, an assembly 1 having spacers andbumpers made of a softer more compressible material than the spacers andbumpers being replaced thereby, also utilizing the same bone screws 4.

FIG. 6 illustrates another embodiment of the dynamic longitudinalconnecting member, generally 102. The connecting member 102 issubstantially identical to the connecting member 2 described above, withthe exception that it includes two cord portions joined by a rodportion. Accordingly, the description of the connecting member 2 isincorporated herein by reference.

The connecting member 102 extends longitudinally along a central axis B,from a first end 106 to a second end 108, with first and secondtransition portions 110 a and 110 b located therebetween. The connectingmember 102 includes three portions, namely a rod portion 112 that joinsa first cord portion 114 a with a second cord portion 114 b. A jacketportion 116 covers the rod and cord portions 112, 114 a and 114 b,similar to the jacket portion 16 described above. The length of theconnecting member 102 is sufficient for engagement by at least threebone attachment members 4, such as those described above. Typicalarrangements of the connecting member 102 include but are not limited toa rod portion 112 with a length sufficient for engagement by one, two,three or more bone anchors 4, joining first and second cord portion 114a and 114 b, each cord portion including a length sufficient forengagement by one, two, three or more bone anchors 4. In an exemplaryembodiment, the rod portion 112 includes a length sufficient forengagement by a single bone anchor 4, and the first and second cordportion 114 a and 114 b each include a length sufficient for engagementby either one or two bone anchors 4. In another exemplary embodiment,the rod portion 112 includes a length sufficient for engagement by twobone anchors 4, and the first and second cord portion 114 a and 114 balso each include a length sufficient for engagement by two bone anchors4. Additional combinations of rod and cord portion 112, 114 c and 114 blengths is foreseen.

The connecting member 102 is substantially cylindrical with one or morecircular cross-sections along a length thereof. However, it is foreseenthat the connecting member 102 may have other forms, including but notlimited to oval, square and rectangular cross-sections as well as othercurved or polygonal shapes.

The diameter of the connecting member 102 is uniform along its entirelength, and sufficient for engagement by the attachment members 4.However, as described above, the cord portions 114 a and 114 b mayinclude optional tapered portions or extension that may aid in theimplantation procedure. Such tapered extensions are typically removedwhen the cords 114 a and 114 b are cut to the final length.

The rod portion 112 is substantially identical to the rod portion 12 ofthe connecting member 2, with the exception that rod portion 112 extendsfrom the first transition portion 110 a to the second transition portion110 b. The rod portion 112 includes a plurality of rodlets 120fabricated as described above with reference to the rodlets 20, andwhich may be joined together by a binding material and/or by filamentousstructures similar to those described above. The rod portion 112 issubstantially rigid, cylindrical and smooth, and includes a lengthsufficient for engagement by at least one, preferably at least two boneattachment members 4, such as described elsewhere herein.

The first cord portion 114 a is substantially identical to the cordportion 14 of the connecting member 2, with the exception that the firstcord portion 114 a extends from the first end 106 to the firsttransition portion 110 a. The first cord portion 114 a includes aplurality of strands 126 fabricated as described above with reference tothe strands 26. The first cord portion 114 a is substantially flexible,cylindrical and smooth, and includes a length sufficient for engagementby at least one, preferably at least two bone attachment members 4, suchas described elsewhere herein. The first cord portion 114 a may be cutto length during implantation by the surgeon.

The second cord portion 114 b is substantially identical to the firstcord portion 114 a and to the cord portion 14 of the connecting member2, with the exception that the second cord portion 114 b extends fromthe second transition portion 110 b to the second end 108. The secondcord portion 114 b includes a plurality of strands 126 fabricated asdescribed above with reference to the strands 26. The second cordportion 114 b is substantially flexible, cylindrical and smooth, andincludes a length sufficient for engagement by at least one, preferablyat least two bone attachment members 4, such as described elsewhereherein. Similar to the first cord portion 114 a, the second cord portion114 b may include an extra length and/or optional tapered portion formanipulating the connecting member 102 during the implantation procedure102, and may be cut to length during implantation by the surgeon.

The cord portions 114 a and 114 b may be joined with the rod portion 112in various ways. In an exemplary embodiment, the bundled strands 126 ofthe first and/or second cord portions 114 a and/or 114 b may abut and besecured to the rod portion 112, such as at the transition portions 110 aand 110 b, respectively. In another exemplary embodiment, the strands126 extend into and optionally through the rod portion 112. For example,the strands 126 of the first portion 114 a may extend from the first end206, through the first transition portion 110 a, and at least partiallythrough the rod portion 112. In some circumstances, the strands 126 mayextend all of the way through the rod portion 112, from the first end206 to the second transition portion 110 b; such that the strands 126 ofthe first cord portion 114 a are also the strands 126 of the secondportion 114 b. In still other circumstances, the strands 126 extend allthe way, from the first end 206 to the second end 208. And, in yetanother example, the strands may extend through the second cord portion114 b, from the second end 208 to the transition portion 110 b, and thenat least partially through, the rod portion 112. In some circumstances,the strands 126 may extend all of the way through the rod portion 112,from the second end 208 to the second transition portion 110 a.Optionally, the strands 126 of the first and/or second cord portions 114a and/or 114 b replace, or are, fibers within the rod portion 112, so asto hold and/or bind the rodlets together.

The jacket portion 116 is substantially identical to the jacket portion16, the description of which is incorporated herein by reference. Thejacket portion 116 extends from the first end 106 to the second end 108and provides a substantially smooth surface to the connecting member102. The jacket portion 116 is substantially strong and flexible, ableto block substantial fraying over the lifetime of the implant. In someembodiments, the jacket portion 116 is a woven or braided structure. Inother embodiments, the jacket portion 116 is a non-woven web of fibers.In still other embodiments, the jacket portion 116 is a tough, resilientmembrane deposited on, and optionally bonded to, the connecting member102. In order to have low or no wear debris, the jacket portion 116outer surface may be coated with an ultra thin, ultra hard, ultra slickand ultra smooth coating, such as may be obtained from ion bondingtechniques and/or other gas or chemical treatments. It is further notedthat inner surfaces of sleeves and/or bone attachment members thatreceive the connecting member 102 may also be likewise coated to providea slick, low to no wear debris interface with the connecting member 102.

FIGS. 7-8 illustrate another embodiment of a dynamic longitudinalconnecting member 202 according to the invention. The connecting member202 is similar to the connecting members 2 and 102, the descriptions ofwhich are incorporated herein by reference.

The connecting member 202 is a longitudinally extending rod-shapedstructure, with a longitudinal axis C, first and second end 206 s and208, a transition portion 210, and two rod portions joined at thetransition portion 210, a substantially rigid first rod portion 212 anda substantially elastic second rod portion 214. The connecting memberlength is sufficient for engagement by two or more bone anchors 2.Similar to the connecting member 2, the connecting member 202 issubstantially cylindrical, with a circular cross-section. However, it isforeseen that the connecting member 202 may have other forms, includingbut not limited to oval, square and rectangular cross-sections as wellas other curved or polygonal shapes. The diameter of the connectingmember 202 is substantially constant or uniform along its length, andsufficient to be matingly engaged by a bone anchor 4, as describedelsewhere herein.

The first rod portion 212 is substantially rigid and runs parallel alongthe axis C, from the first end 206 to the transition portion 210. Aplurality of long, thin and cylindrical rodlets, some of which aredenoted by the numerals 220A, 220B, 220C and 220D, are aligned with theaxis C and extend from the first end 206 to the transition portion 210.The rodlets 220A, 220B, 220C and 220D include a substantially circularcross-section with substantially equal diameters.

The rodlets 220A, 220B, 220C and 220D are fabricated similarly to thoseof the rod portion 12, such as from a variety of materials ranging inhardness and elasticity from deformable plastics to hard metals,depending upon the desired application. Suitable materials include, butare not limited to metals, metal alloys and deformable and lesscompressible plastics, including, but not limited to metal and metalalloys including but not limited to stainless steel, titanium, titaniumalloys and cobalt chrome; or other suitable materials, including plasticpolymers such as polyetheretherketone (PEEK), ultra-high-molecularweight-polyethylene (UHMWP), polyurethanes and composites, includingcomposites containing carbon fiber, natural or synthetic elastomers suchas polyisoprene (natural rubber), and synthetic polymers, copolymers,and thermoplastic elastomers, for example, polyurethane elastomers suchas polycarbonate-urethane elastomers. It is foreseen that some or all ofthe rodlets 220A, 220B, 220C and 220D may be deformable and/or of adifferent cross-sectional geometry. Further, it is foreseen that thegeometry and fabrication material of the individual rodlets 220A, 220B,220C and 220D may be varied such that, when bundled together, the rodportion 212 is provided a desired level of rigidity or flexibility.

As is most easily seen in FIG. 8, the rodlets 220A, 220B, 220C and 220Dare spaced from each other and embedded in a polymer material or matrix222 , such as but not limited to plastic polymers such aspolyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene(UHMWP), polyurethanes and composites, including composites containingcarbon fiber, natural or synthetic elastomers such as polyisoprene(natural rubber), and synthetic polymers, copolymers, and thermoplasticelastomers, for example, polyurethane elastomers such aspolycarbonate-urethane elastomers. The polymer is shaped such that anexterior surface 223 a of the first rod portion 212 is substantiallycylindrical and smooth. In order to have low or no wear debris, theexterior surface 223 a may be coated with an ultra thin, ultra hard,ultra slick and ultra smooth coating, such as may be obtained from ionbonding techniques and/or other gas or chemical treatments.

The second rod portion 214, sometimes referred to the cord portion, is asubstantially elastic or deformable polymer rod-like structure runningparallel with the axis C, from the transition portion 210 to the secondend 208. The second rod portion 214 includes a diameter that issubstantially uniform along its length, with the exception of anoptional tapered portion at the second end 208. The length of the secondrod portion 214 is sufficient for engagement by at least one boneanchor, and generally includes an extra length used by the surgeonduring the implantation procedure to grasp and pull the connectingmember 202, such as described elsewhere herein.

The second rod portion 214 is formed of an elastomeric polymer materialor matrix, similar to the polymer material 222. In some embodiments, thesecond rod portion 214 and the polymer material 222 are integrallyformed. For example, the rodlets 220A, 220B, 220C and 220D may be placedin a mold that is sized for injection molding both the first and secondrod portions 212 and 214. The mold is then filled with liquid polymerthat is subsequently cured, to yield the completed connecting member202. Alternatively, the first and second rod portions 212 and 214 may befabricated separately, abutted together and then joined at thetransition portion 210, all steps using known manufacturing techniques.

The second rod portion 214 may be fabricated from a variety of elastic,deformable materials. Suitable materials include but are not limited toplastic polymers such as polyetheretherketone (PEEK),ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes andcomposites, including composites containing carbon fiber, natural orsynthetic elastomers such as polyisoprene (natural rubber), andsynthetic polymers, copolymers, and thermoplastic elastomers, forexample, polyurethane elastomers such as polycarbonate-urethaneelastomers. While the second rod portion 214 does not generally includestrands, similar to those described above, in some circumstances, thesecond rod portion 214 does include polymer or mineral fibers, such asdescribed elsewhere herein. Such fibers may strengthen the second rodportion 214, thereby making it better able tow withstand shear andtorsional forces.

The second rod portion 214 is formed of a composite of at least twomaterials. In an exemplary embodiment, thin, longitudinally extendinglayers of two or more polymers of differing durometers may be fusedtogether to provide increased strength or varying flexibility to thesecond rod portion 214. A similar effect may be achieved by fusingtogether thin rods of two or more polymers of differing durometers. Inanother exemplary embodiment, polymers of different durometers may beused along the length of the second rod portion 214, either as discreetlayers or as a continuous transition from one polymer to the next, so asto vary or change the relative rigidity, hardness, flexibility and/ordeformability of the second rod portion 214 along its length. In yetanother exemplary embodiment, concentric layers of two or more polymersmay be formed into the second rod portion 214, such as by alternately orsuccessively applying, such as by dipping spraying, layers of two ormore polymers to a small polymer core structure, with a cure step aftereach application.

The exterior surface 223 b of the second rod portion 214 is shaped so asto be substantially cylindrical and smooth. In order to have low or nowear debris, the exterior surface 223 b may be coated with an ultrathin, ultra hard, ultra slick and ultra smooth coating, such as may beobtained from ion bonding techniques and/or other gas or chemicaltreatments.

While not shown, the connecting member 202 of the invention may be usedwith the same or similar spacers and/or sleeves with cooperatingclosure, as described above with respect to the connecting member 2,especially to protect the transition portion 210 and to provideadditional support to the elastic portions of the connecting member 202.The transition portion 210 is located between two bone anchors 4. Theassembly 1 including the connecting member 202 preferably includes aspacer surrounding the transition portion 202, similar to that describedabove with regards to FIGS. 1-3.

FIGS. 9-12 illustrate yet another embodiment of a dynamic longitudinalconnecting member 302 according to the invention. The connecting member302 is substantially similar to the connecting members 1, 102 and 202,the descriptions of which are incorporated herein by reference.

The connecting member 302 extends longitudinally along the central axisD, from a first end 306 to a second end 308, with a transition portion310 located therebetween. Over all, the connecting member 302 issubstantially cylindrical, with a circular cross-section and a diameterthat is substantially uniform along its length. The connecting member302 includes a length sufficient for engagement by at least two boneanchors 4. For example, in FIG. 12, the connecting member 302 is shownas engaged by four bone anchors 4. The connecting member 302 may be usedin combination with cooperating sleeves and/or spacers, similar to thosedescribed above. The connecting member 302 includes two portions, asubstantially rigid first rod portion 312 and a substantially flexible,elastic second rod portion 314.

Referring to FIGS. 9-12, the substantially rigid first rod portion 312extends a length sufficient for engagement by at least one, preferablyat least two bone anchors 4, and includes an inelastic stent structure320 that is at least partially embedded in an elastomeric polymermaterial 322. The elastomeric polymer material 322 is shaped such that asurface 322A thereof is substantially smooth and uniformly cylindricalalong its entire length. Since the length of the first rod portion 312may be much longer than required in the completed implant assembly 1, ismay be cut to length by the surgeon using methods described elsewhereherein.

The stent structure 320 extends along the axis D, from the first end 306to the transition portion 310. The stent structure 320 includes firstand second ends 320A and 320B. The ends 320A and 320B are generallyannular and may be planar, outwardly curved or contoured. The stentstructure 320 includes a plurality of longitudinally extending concavesurfaces 320C joined by ridge surfaces 320D. In an exemplary embodimentaccording to the invention, the stent structure 320 shown in FIGS. 10and 11 includes five concave surfaces 320C, wherein adjacent concavesurfaces 320C are joined by ridge surfaces 320D. Since the stentstructure 320 is embedded in the polymer 322, spaced defined by theconcave surfaces 320C and the exterior surface of the connecting member302 are substantially filled with the elastomeric polymer material 322.The concave surfaces 320C provide an enlarged surface area for tightlybinding with the elastomeric polymer material 322, for example, suchthat there is substantially no slippage between the two structures. Thelongitudinally extending surfaces 322A of the polymer material 322,which fills the spaces, are convex, outwardly bowed or partiallycylindrical.

The ridge surfaces 320D are slightly convex and substantially flush withthe outer surface 312 a of the first rod portion 312. The surfaces ofthe polymer material 322 are shaped such that together with the ridgesurfaces 320D, a cross-section of the connecting member 302 is circular,thereby providing the cylindrical outer surface of the connecting member302. However, it is foreseen that the ridge surfaces 320D may be othershapes, such as planar. Further, it is foreseen that the ridge surfaces320D may be located slightly above or below the outer surface 312A.

Referring now to FIGS. 10-11, due to the alternating arrangement of theconcave and ridge surfaces 320C and 320D, the stent structure 320 has agenerally star or starfish-shaped cross-section. For example, theillustrated embodiment has a five-armed starfish shaped cross-section.However, it is foreseen that the stent structure 320 could have more orfewer concave surfaces 320C and ridge surfaces 320D, thereby giving thecross-section more or fewer “arms” than are shown in FIGS. 10-11. It isnoted that the widest diameter, or width of the cross-section is aboutequal to the diameter of the connecting member 302.

The stent structure 320 includes a longitudinally extending through-bore320E, which extends from the first end 320A to the second end 320B. Thethrough-bore 320E is coaxial with the axis D. The through-borecross-section is substantially circular. However, it is foreseen thatthe cross-section may have other shapes, such as ovular, rectangular, oreven irregular. The through-bore 320E is substantially filled with theelastomeric polymer material 322.

A plurality of spaced perpendicular bores 320F extend radially throughthe stent structure 320, so as to join the concave surfaces 320C withthe lumen, or internal surface, of the through-bore 320E. As shown inFIG. 9, a plurality of perpendicular bores 320F are spaced along thelength of each concave surface 320C. Further, the perpendicular bores320F of a first concave surface 320C are staggered with respect to theperpendicular bores 320F of the adjacent concave surfaces 320C. Theperpendicular bores 320F are also substantially filled with theelastomeric polymer material 322, said material 322 being integral withthe material 322 filling the through-bore 320E.

The stent structure 320 is embedded in the elastomeric polymer material322, which fills the spaces of the concave surfaces 320C, thethrough-bore 320E and the perpendicular bores 320F. The material fillingall of these spaces or elements is substantially integrally formed.Suitable polymer materials 322 include but are not limited to plasticpolymers such as polyetheretherketone (PEEK), ultra-high-molecularweight-polyethylene (UHMWP), polyurethanes and composites, includingcomposites containing carbon fiber, natural or synthetic elastomers suchas polyisoprene (natural rubber), and synthetic polymers, copolymers,and thermoplastic elastomers, for example, polyurethane elastomers suchas polycarbonate-urethane elastomers. In order to have low or no weardebris, the convex outer surface 312 a may be coated with an ultra thin,ultra hard, ultra slick and ultra smooth coating, such as may beobtained from ion bonding techniques and/or other gas or chemicaltreatments.

The second rod portion 314 is a substantially elastic, substantiallycylindrical rod that extends from the transition portion 310 to theconnecting member second end 208. The second rod portion 314 has asmooth and convex, or cylindrical, outer surface 314 a and asubstantially circular cross-section. The diameter of the second rodportion 314 is substantially uniform, or constant, along its entirelength, and sufficiently sized such that second rod portion 314 isreceivable or engageable by a bone anchor 4. The second rod portion 314includes a length sufficient for engagement by at least one, preferablyat least two bone anchors 5. Generally, the second rod portion 314 islonger than is required in the completed implant assembly 1, and is cutto length by the surgeon. The extra length of the second rod portion 314may be used by the surgeon in tensioning the second rod portion 314.

The second rod portion 314 is formed of an elastomeric polymer material322, such as but not limited to plastic polymers such aspolyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene(UHMWP), polyurethanes and composites, including composites containingcarbon fiber, natural or synthetic elastomers such as polyisoprene(natural rubber), and synthetic polymers, copolymers, and thermoplasticelastomers, for example, polyurethane elastomers such aspolycarbonate-urethane elastomers. In order to have low or no weardebris, the outer surface 314 a, of the second rod portion 314, may becoated with an ultra thin, ultra hard, ultra slick and ultra smoothcoating, such as may be obtained from ion bonding techniques and/orother gas or chemical treatments.

In some embodiments, the second rod portion 314 is integrally formedwith the material in which the stent structure 320 is embedded, andwhich therefore fills the concave surfaces 320C, the through-bore 320Eand perpendicular bores 320F. In an exemplary embodiment, the connectingmember 302 is fabricated by placing the stent structure 320 in aninjection mold sized and shaped to form the completed connecting member302. The mold is filled with a liquid polymer material 322, that issubsequently cured, thereby forming the completed connecting member 302.Alternatively, the first and second rod portions 312 and 314 may befabricated separately, abutted and joined in the completed connectingmember 302.

Referring now to FIG. 12, the connecting member 302 may be engaged by aplurality of bone anchors 4. In the illustrated embodiment of theinvention, the connecting member 302 is engaged by four bone anchors 4.Two of the bone anchors 4 engage the first rod portion 312, and theremaining two bone anchors 4 engage the second rod portion 314. It isnoted that the transition portion 310 is located between the two inboardbone anchors 4. An elastomeric spacer 160 is located between, and abuts,the two inboard bone anchors 4, thereby protecting the transitionportion 310 and reinforming, or supporting, the connecting member 302.Another spacer 160 is located between, and abuts, the two right-handbone anchors 4, as shown in FIG. 12. This second spacer lends additionalstrength and rigidity to the second rod portion 314. An optional thirdspacer 160 may be located between the two left-hand bone anchors 2. Theclosures used with the outboard bone anchors 4 are gripping closures,such as point and rim closures, so as to firmly lock the connectingmember 302 with respect to the bone anchors 4. The closures used withthe inboard bone anchors 4 may be either gripping closures or slidingclosures. As discussed above, such sliding closures allow somelongitudinal sliding of the connecting member 302 with regards to thebone anchor 4.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

1. In a medical implant assembly having at least two bone attachmentstructures cooperating with a dynamic longitudinal connecting member,the improvement wherein the connecting member comprises: a) a first end,a transition portion and a second end; b) a rod portion extendinglongitudinally from the first end to the transition portion, andincluding a longitudinal axis and a substantially rigid core runningsubstantially parallel with the longitudinal axis; c) a tensionable cordportion joined with the rod portion and extending from the transitionportion to the second end; and d) a substantially flexible jacketportion covering the rod and cord portions.
 2. The improvement of claim1 wherein the rod portion includes a plurality of substantially rigidlongitudinally extending rodlets.
 3. The improvement of claim 2 whereinthe rod portion includes a binding material adapted for joining therodlets together.
 4. The improvement of claim 2 wherein the rod portionincludes a plurality of filamentous structures.
 5. The improvement ofclaim 4 wherein the filamentous structures at least partially surroundthe rodlets.
 6. The improvement of claim 4 wherein the filamentousstructures are substantially flexible.
 7. The improvement of claim 6wherein the filamentous structures include at least one polymer.
 8. Theimprovement of claim 1, wherein the cord portion is in tension.
 9. Theimprovement of claim 1, wherein the cord portion includes a plurality ofsubstantially flexible strands extending from about the transitionportion towards the second end.
 10. The improvement of claim 9 whereinthe strands are braided.
 11. The improvement of claim 9 wherein thestrands are coiled.
 12. The improvement of claim 9 wherein the strandsare random.
 13. The improvement of claim 9 wherein the strands areembedded in an elastomer.
 14. The improvement of claim 9 wherein thestrands include a polymer.
 15. The improvement of claim 9 wherein thestrands include a mixture of a polymer and a plurality of at least oneof fibers and filaments.
 16. The improvement of claim 1 wherein the cordportion comprises a substantially elastic polymer filament.
 17. Theimprovement of claim 1 wherein the cord portion comprises a polymer rod.18. The improvement of claim 17 wherein the polymer rod includes asubstantially elastic polymer.
 19. The improvement of claim 17 whereinthe polymer rod includes a composite of at least two polymers.
 20. Theimprovement of claim 1 wherein the cord portion includes a flexiblecable.
 21. The improvement of claim 1 wherein the cord portion includesa flexible cord.
 22. The improvement of claim 1 further comprising aspacer covering the transition portion.
 23. The improvement of claim 22wherein the spacer extends between the at least two bone attachmentstructures.
 24. The improvement of claim 22 wherein the spacer issubstantially elastic.
 25. The improvement of claim 1 further comprisinga sleeve located between the cord portion and one of the at least twobone attachment structures.
 26. The improvement of claim 25 wherein thesleeve includes a through-bore in sliding engagement with the cordportion.
 27. The improvement of claim 1 wherein the rod portioncomprises an inelastic stent structure at least partially embedded in anelastomer.
 28. The improvement of claim 24 wherein the rod portionincludes a substantially cylindrical outer surface; and the stentstructure includes a longitudinally extending lumen and a plurality oflongitudinally oriented concave grooves adapted for contacting theelastomer.
 29. The improvement of claim 28 wherein the stent structureincludes a plurality of bores extending radially from the lumen to oneof the plurality of concave grooves.
 30. The improvement of claim 29wherein the cord portion includes a substantially flexible rod formed ofthe elastomer; and wherein the elastomer fills the lumen and the bores.31. The improvement of claim 1 further comprising an elastic bumper anda cord blocker.
 32. In a medical implant assembly having at least twobone attachment structures cooperating with a dynamic longitudinalconnecting member, the improvement wherein the connecting membercomprises: a) a first end, a transition portion and a second end; b) thefirst end includes a rod portion extending longitudinally from thetransition portion; c) the second end includes a cord portion joinedwith the rod portion at the transition portion and extendinglongitudinally therefrom; and d) a substantially flexible jacket portioncovering the rod and cord portions and extending over an entire lengthof the transition portion.
 33. In a medical implant assembly having atleast two bone attachment structures cooperating with a dynamiclongitudinal connecting member, the improvement wherein the connectingmember comprises: a) a first end, a transition portion and a second end;wherein i) the first end includes a substantially solid rod portionhaving an axis and extending longitudinally from the transition portion;and ii) the second end includes a tensionable cord portion joined withthe rod portion at the transition portion and extending from a positionwithin the transition portion coaxially and longitudinally therefrom; b)a sleeve; c) and a spacer; wherein d) at least one bone attachmentstructure is secured to the substantially solid rod portion, the spaceris positioned between the at least two bone attachment structures, thesleeve is secured to at least one bone attachment structure and thespacer at least partially overlaps the sleeve.
 33. In a medical implantassembly having at least two bone attachment structures cooperating witha dynamic longitudinal connecting member, the improvement wherein theconnecting member comprises: a) a first end, a transition portion and asecond end; b) a rod portion extending longitudinally from the first endto the transition portion, and including a longitudinal axis and asubstantially rigid core running substantially parallel with thelongitudinal axis; c) a tensionable cord portion joined with the rodportion and extending from the transition portion to the second end; d)a flexible spacer portion at least partially covering the transitionportion and positioned between the at least two bone anchors; e) abumper engaging the tensionable cord; and f) a blocker engaging thetensionable cord.
 34. The improvement according to claim 33, wherein a)the bumper engages one of the at least two bone anchors.
 35. Theimprovement according to claim 33, wherein a) the blocker engages one ofthe at least two bone anchors.
 36. The improvement according to claim33, wherein a) the blocker engages the bumper.